Add preserve_existing param to Indices/PutSettings whitelist

Author: polyfractal

src/Elasticsearch/Endpoints/Indices/Settings/Put.php

@@ -59,6 +59,7 @@ protected function getParamWhitelist()
             'allow_no_indices',
             'expand_wildcards',
             'flat_settings',
+            'preserve_existing'
         );
     }